1. Field of the Invention
The present invention relates to a method of fabricating metal interconnects and inter-metal dielectric layer thereof, and more particularly, to a method of fabricating a thick metal interconnect layer with reduced resistance, and a method of fabricating a thick inter-metal dielectric layer.
2. Description of the Prior Art
Metal interconnects, which are disposed over electronic devices, are responsible for transmitting signals sending from electronic devices and for transmitting external signals to electronic devices, and therefore the resistance of metal interconnects is critical to the transmission speed. A high resistance of metal interconnects will reduce the transmission speed, thereby degrading the response time and increasing power consumption of electronic products.
According to basic electronics theorem, the resistance of a conducting wire is inversely proportional to its cross-sectional area. Therefore, the thicker the metal interconnect is, the lower the resistance is. Conventionally, the metal interconnects are multilevel interconnects fabricated by a copper damascene process. A copper damascene process includes the following steps. First, an inter-metal dielectric layer is formed, and trenches are formed in the inter-metal dielectric layer. Subsequently, a copper metal layer is formed on the inter-metal dielectric layer, filling the trenches. Thereafter, a CMP process is performed to remove the copper metal layer outside the trenches. The above steps are repeated to form multilevel copper interconnects. Since each copper metal interconnect layer requires one CMP process, the cost is increased and the yield may be affected. In addition, there are two methods to fabricate inter-metal dielectric layer: one method forms BPSG glass on the wafer first, and planarizes BPSG glass by thermal reflow to form a silicon oxide layer; the other method uses SOG process to coat dielectric material dissolved in a solvent on the wafer, and removes the solvent by thermal treatment to form a silicon oxide layer. However, the dielectric constant of the inter-metal dielectric layer formed by the conventional methods is not able to meet the electrical requirements of some types of electronic devices e.g. high frequency devices or MEMS devices.